Continuous and accurate monitoring of radioactive emissions within particular areas is known to be, in certain cases, of both sanitary and scientific interest.
For sanitary purposes, as defined by many national and local regulations, such detections are performed in the air of spa resorts, where the concentration of radioactive particles can considerably change throughout the various steps of the activity. For the same reasons, radon exhalation is required to be detected and monitored in tunnels, mines and underground laboratories, and radiation emission levels must be monitored in any site that involves a high exposure risk, such as nuclear power stations or anyway operating reactors.
For scientific purposes, particularly relating the study of geophysics, monitoring of radon concentration in the ground is important for correlating it, for instance, to seismic and/or volcanic activity in certain zones.
As a matter of fact, it is known that, of the radioactivity that is found over a site, the highest contribution is given by the presence of radioactive gases, such as radon (222Rn) and thoron (220Rn), of local origin, which are the expression of natural emissions from the ground or the area to be monitored.
Nonetheless, in the above monitoring activities in addition to in situ 222Rn, i.e. generated by its precursor radionuclides within a confined area proximate the measuring point, it is especially important to detect the remote origin fraction, i.e. emitted far from the place of measurement, which is more difficult to estimate. Such fraction may be sometimes deemed to be a useful parameter for studying abnormal geophysical phenomena. In this respect, it would be very useful to isolate the local fraction of 222Rn from the total detected amount, which might also be greater than the remote origin fraction.
For this purpose, adequate measuring instruments are required, which combine continuous radon detection over a site with an analysis method that allows to determine remote origin gas fraction from the measurements and from careful prior characterization of the site.
A number of radioactive monitoring instruments are known which are able to differentiate individual nuclide contributions. These known instruments use spectroscopic analysis as well as methods for estimating background radiation interference in the accuracy of measurement. Most of these instruments provide simultaneous measurement, within the detection apparatus, of certain ambient parameters, whose values might affect the efficiency and accuracy of individual nuclide detection. However, none of them uses a method that allows differentiation of remote and local radon fractions.
For example, patents GB 2 428 088 and GB 2 428 291 disclose apparatus that use methods for detecting alpha or beta particles deriving from uranium or transuranic elements, in which measurement is generally affected by the interference of isotopes such as radon and thoron of “natural” origin. In an attempt to correct such measurement detection of air pressure and temperature within the detector has been proposed, whose values influence the measured spectrum. Nonetheless, in the above mentioned apparatus radon isotopes are only measured as measurement interference factors, whose contribution has to be subtracted from measurement.
The apparatus of GB 2 368 185 and WO 2006/070139 similarly use sensors for detecting temperature and pressure within the measuring instrument and in the ground in which radon concentration is to be measured. However, this technique does not allow to differentiate local and remote origin radon contributions.